The unglossed headword occurs only here, but its meaning is plain enough. The pentekoste -- literally the fiftieth --was a 2% tax, attested in classical Athens and elsewhere, and the pentekostologos the man who collected it. See pi 983 (and LSJ s.v.).
[1] Quotation unidentifiable -- and also surely incomplete: a phrase such as 'to the place' needs to be supplied. (For a parallel, of sorts, see Demosthenes 25.57, on Aristogeiton and Zobia: labw\n au)to\s au)toxeiri/a| pro\s to\ pwlhth/rion tou= metoiki/ou a)ph/gage.)